A major need exists for new or improved vaccines including prophylactic vaccines for potential bioterrorism infectious organisms and therapeutic vaccines such as for cancer. For example, mailed powder containing anthrax material killed unsuspecting office workers and caused major disruption due, in part, to lack of a good and safe vaccine. The migration of avian flu is a major concern given lack of an effective vaccine. There exists a need for rapid development of vaccines toward emerging infectious agents such as SARS or bioterrorism developments. Therapeutic vaccines also are needed.
Anthrax is an infectious bacterial disease caused by Bacillus anthracis and occurs in domestic animals and humans exposed to infected animals, tissue, or spores. The virulence of B. anthracis is dependent on Anthrax Toxin (AT) and poly-gamma-D-glutamic acid capsule (PGA). PGA provides the bacteria a way to evade immune cells by providing a ‘stealth’ cover. PGA also is not very immunogenic. AT is composed of three entities: Protective Antigen (PA) (the binding subunit of AT), Lethal Factor (LF) and Edema Factor (EF) (Mikesell et al., Infect. Immun. 39:371-76, 1983; Vodkin et al Cell 34:693-97, 1983). PA is an 83 kDa protein that is the main protective constituent of anthrax vaccines. A currently approved human vaccine for Anthrax, which is manufactured from a cell free extract of un-capsulated Bacillus Anthracis (AVA, BioPort Corporation, Lansing Mich.), has several limitations including a requirement for six vaccinations over eighteen months followed by yearly boosters (Pittman et al., Vaccine 20:1412-20, 2002; Pittman et al., Vaccine 20:972-78, 2001) and is associated with undesirable reactions (Pittman et al., Vaccine 20:972-78, 2001). PA is necessary for vaccine immunogenicity (Ivins et al., Infect. Immun. 60:662-68, 199 Welkos and Friedlander, Microb. Pathog. 5:127, 1998) and can inhibit germination of spores (Welkos eta., Microbiology 147:1677-85, 2001). Current efforts for development of a new vaccine focus on using PA as the antigen. In order to have an effective prophylactic vaccine against capsulated bacteria and its toxin, a combined immune response against PA and the PGA will be advantageous. Late stage clinical development by VaxGen of an experimental vaccine based on recombinant PA has been put on hold.
Anthrax toxins are formed by PA, lethal factor (LF), and edema factor (EF), which are secreted separately as nontoxic monomers. Binding of LF or EF to PA produces active toxin. PA along with bound LF or EF is internalized by cells by receptor mediated endocytosis in a heptameric form. In the endosome, PA undergoes a pH-induced conformational change, producing a pore in the endosomal membrane permitting toxin translocation into the cytoplasm and toxicity. The conjugation of PA to gamma-D-PGA has been suggested as a means to obtain simultaneous immune responses (Rhie et al. PNAS 100, 10925 2003, Schneerson et al. WO 2005/000884). Antigenic constructs that can provide presentation of PA and PGA to antigen presenting cells and also prevent the multimerization and pore formation of PA molecules, will be advantageous in preventing the infection and the effect of toxin.
Many viral infections are not managed adequately, requiring new or better vaccines, including avian flu. The major viral antigens of influenza, including N, HA, and M proteins, change rapidly, limiting the benefit of each vaccine. Also current production relies on growth in eggs with severe commercial limitations. An effective and safe vaccine not dependent on biological manufacturing and that is rapidly adaptable for rapidly changing antigens is needed.
The purpose of a therapeutic vaccine is not only to induce an immune response but to induce a response that is beneficial for patients already exposed to an infectious agent or who have ongoing infection or disease. One major interest for potential application of therapeutic vaccines is for treatment of cancer patients. However, commercially successful products have encountered several hurdles, including the difficulty of identifying antigens, finding antigens that are broadly applicable, and identifying adjuvants that achieve an effective immune response. Despite the recent achievements using nanoparticles to improve immune response, a need clearly exists for more effective and safe prophylactic and therapeutic vaccines as well as further improvements in nanoparticles to address needed capabilities.
Most candidate therapeutic classes, from large proteins such as antibodies, to small molecules such as chemotherapy, are limited by pharmacological barriers that potentially can be overcome using drug delivery. Production of pharmaceutically active polypeptides and nucleic acids is adequate (Biomacromolecules 2004; 5:1917-1925), but their use remains limited by many barriers, including absorption, diffusion into cells, degradation, etc. (J. Control. Release 1996; 39:131-138). Small molecules also can face similar barriers, such as toxicity from widespread biodistribution, and these severely limit their development as seen by annual decreases in new drug approvals even though delivery systems often are incorporated. Another growing clinical need is for combinations of approved products, again pointing to a need for better delivery systems with capabilities for two or more active ingredients.
Nanoparticles have benefited several commercialized therapeutics, but the extensive research revealed numerous barriers and challenges hampering further application. Major challenges include a need for better manufacturing, control of particle size and homogeneity, cargo loading, cargo release at the target cell or tissue, biocompatibility, and disease selectivity. Improvement is needed for broad commercial application.
Hydrophilic polymer conjugates of active ingredients to improve pharmacological activity have been reported. These materials are nanoscale but are soluble and thus are not nanoparticles. Commercialization limitations include a need for all functions, such as targeting ligands, to be coupled effectively to the large carrier and difficulty for the carrier to meet all the strict regulations applied to the active ingredient, exacerbated as the carrier size increases. Adaptation of hydrophilic carriers for use in nanoparticles has been disclosed frequently by conjugation with poorly soluble material such as lipids, polylactides, etc., and further comprising association of active ingredient either covalently or non-covalently. In this case the conjugate forms or associates with a micelle, liposome, or solid colloid. A limitation of such compositions is that to obtain the nanoparticle benefits, the carrier mass and components is increased, reducing commercial utility due to increased costs, lower drug loading, great product heterogeneity. Although development of nanoparticles has led to improved products, the current compositions fail to address the needs of many vaccine and therapeutic applications. Therefore, a need exists for effective and safe vaccines and therapeutics.